Boost the nutrients in your garden soil now, but don’t use chemical fertilizers

By Jeff Lowenfels

Updated: September 15, 2022 Published: September 15, 2022

One of the reasons people still cling to chemical fertilizers is because they go to work quickly. Organic fertilizers, on the other hand, usually take time for the microbes to break it down. Sometimes this can take months. This is why now is the time to apply such things to your soils so that they can benefit next year’s crops.

There are several ways to do this. The first assumes all was well this year and your plants thrived and didn’t show nutrient deficiencies. You can probably forgo a soil test for nutrients. Apply an inch or two of compost or vermicompost to the surface of all of your containers and on your garden beds. You can do it now, even though there are plants still performing.

This can be followed with an application of mulch (once enough leaves fall). I like to run ours over with a mower first as the finer the mulch, the quicker the microbes decay it and return goodies to the soil. More specifically, there will be more bacteria when things are mulched up and these produce the kind of nitrogen annuals and vegetables like.

Note that sometimes too much of a good thing is not a good thing. Too much compost can result in phosphorous overload which can cause problems with pH and some nutrients’ uptake. An inch or two is fine and all your soils need. Planting in pure compost is not a good idea and can result in stunted plants.

This leads to the second method of adding nutrients. It assumes your gardens did not do well so you need to be concerned about specific nutrients and your soil’s pH. The only way to tell what is needed is to have a soil sample analyzed by a professional lab.

The Cooperative Extension has suggestions for you when it comes to testing soil samples and if you just want to find a testing laboratory, they have provided a list. It is important that you tell whatever lab you use that you are an organic gardener (you are, right?) and that you want recommendations in that vein.

I am not naive enough to believe all Alaskan gardeners will rush out and get their garden soil tested. Just remember the Law of Return. You remove from your gardens things that should decay and return nutrients to the soil. So at the very least you need to put something back into the system so it will operate properly.

Given the Law of Return, consider the nonharvested parts of the plants left in your gardens. On the one hand those cabbage stems might be moose fodder, but on the other hand, leaving the root, stems and leaves to decay makes violating the Law of Return a they gardening misdemeanor instead of pulling everything and then rototilling things clean which is definitely a gardening felony.

Finally, I advise a company that produces a cellphone-based testing kit that allows you to know if your efforts are really “team with microbes” and are improving your soil. The kit measures microbial biomass which correlates with soil fertility, especially the all-important nitrogen component. A test now and one late spring should show an increase in biomass if you compost/mulch now. For $5 or so, you can check your soil’s pH and biomass at home in about 10 minutes. Check it out at

Jeff’s Alaskan Garden Calendar:

Mushroom Kit Workshop: Alaska Botanical Garden, Tuesday, Sept. 20; 5-7 pm Learn to grow your own mushrooms! Join the owners of Far North Fungi, Allison and Gabe, for a hands-on workshop on growing oyster mushrooms.

Brussels sprouts: These get sweeter the cooler it gets (up to a point!) so wait until the first frost if you can.

Potatoes: Once the leaves are yellow, you can harvest. Again, waiting for real cool weather produces a sweeter spud.

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